1. Field of the Invention (Technical Field)
The present invention relates to an improved automatically extendable and retractable center stand for motorcycles, an improved linear actuator, and methods for using such stand and actuator.
2. Background Art
Stands for motorcycles are essential in parking the motorcycles. The well known side-mounted "kick" stand, although expedient and easy to operate, presents only one-point surface contact. On ground surfaces comprising soft sand, hot asphalt, oil slicks, or the like, the likelihood of upsetting the motorcycle is great.
Center stands for motorcycles offer an alternative parking mechanism to motorcycle riders. However, although the center stand offers a more stable two-point surface contact, it can be cumbersome and difficult to operate. The center stand must be pressed against the ground surface by overcoming an upwardly-exerted spring force (usually by standing on it), while the motorcycle is rocked backwardly, using the stand as a fulcrum. This involves strength and agility not possessed by all riders. Also the rider must dismount the motorcycle in order to engage the center stand. In view of the fact that many of today's fully equipped touring motorcycles weigh upwards of 800 pounds, many riders will opt to use the easily engaged, less stable side stand. Concomitantly, the more stable center stand is used only rarely, if at all.
Center stands are disclosed in the following references. U.S. Pat. No. 1,039,838, to Steinberger, entitled, "Motor Cycle Stand," discloses a rear wheel mounted center stand, apparently manually extended, which is retracted and locked into the traveling position by forward motion of the motorcycle.
U.S. Pat. No. 4,432,562, to Cline, entitled, "Motorcycle Jack Stand" and U.S. Pat. No. 4,580,804, to Weber, entitled, "Jack Stand for Motorcycles" apparently both teach motorcycle center stand structures wherein the legs of the stand are manually (or pedally) pivoted downwardly and then telescopically extended.
U.S. Pat. No. 4,693,488, to Bernocco, entitled, "Electrically Controlled Motorcycle Stand" discloses a center stand structure rotatable downwardly into the operative position by an electric motor and gear assembly.
U.S. Pat. No. 4,513,837 to Archer, entitled, "Motorcycle with Outrigger Wheels" discloses hydraulically or pneumatically actuated outrigger wheels to provide lateral support.
U.S. Pat. No. 4,660,847 to Yagasaki, entitled, "Main Stand Device for Two-Wheeled Motorcycle" teaches a center stand structure manually rotatable downwardly having a motor-driven telescoping leg.
Another motorcycle lift stand of interest is that disclosed in Japanese reference 1-262272, entitled "Stay Stand Device for Motorcycle", to Fujita, which teaches a stand initially driven by manual force, then motor driven to an upright position.
Japanese reference 2-3585, entitled "Auxiliary Wheel Device for Motorcycle", to Uehara discloses a drive circuit for adjusting the height of "training wheels" on a motorcycle.
German reference DE 3401740A1 entitled "Parking Stand for Motor Cycles" to Hanle, discloses a spindle-driven stand for motorcycles.
U.S. Pat. No. 4,693,488, entitled "Electrically Controlled Motorcycle Stand", to Bernocco, discloses a pinion-gear driven motorcycle stand.
Perhaps most relevant is Australian reference 280,268, to Harrison, entitled "Improvements in Two-Wheeled Motor Vehicles". This reference discloses a spring actuated bilaterally-mounted motorcycle lift stand which provides motorcycle re-erection from whichever side it rests, as well as providing a normal parking stand capability. This reference, however, teaches only direct spring actuation; such spring only being compressed by hydraulic pressure.
The prior art is also replete with ball screw linear actuators. Such actuators normally consist of threaded co-acting concentric telescoped relatively rotating members having a plurality of balls therebetween. Relative rotation between members results in linear translation of the members.
U.S. Pat. No. 3,404,580, to Valenti, entitled "Ball Screw Actuator", discloses a ball screw linear actuator having a plurality of concentric members. However, the ball recirculating tubes are external of the member, thereby resulting in larger, nonuniform diameters of such members.
U.S. Pat. No. 3,404,581, to Kraus, entitled "Ball Screw Actuator" discloses similar structure.
U.S. Pat. No. 2,975,649, to Propst, entitled "Ball Screw Assembly with Internal Ball Return"; U.S. Pat. No. 3,068,714, to Davis, entitled "Nut and Screw Drive Device of the Recirculating Ball Type"; and U.S. Pat. No. 3,537,666, to Lewis, entitled "Retractor for Seatbelts and the Like"; all teach two-member ball screw linear actuator structure with internal ball return tubes or channels.
Soviet Union Patent No. 261071 discloses a single recirculating groove for a ball screw linear actuator having two coacting members.
None of the cited ball screw actuator patents, however, disclose at least three coacting telescoped members, the intermediate member having both an internally grooved portion and a single externally grooved ball recirculating portion. Nor, of course, does the prior art teach the use of a plurality of such ball screw actuators in a motorcycle lift stand.